1. Field of the Invention
The present invention relates to an oral skin improving agent to be orally administered or ingested, a skin improving method and a food composition for improving skin, for improving the skin condition of humans.
2. Description of the Related Art
Hyaluronic acid, which is classified as a polysaccharide having as constituent repeating units the two saccharides, glucuronic acid and N-acetylglucosamine, is a high molecular weight substance that is synthesized in the body, has an extremely high water holding capacity, and is known to play an important role in the elasticity and suppleness of the skin (particularly the corium).
The amount of hyaluronic acid in skin cells decreases with age, and accompanying this the elasticity and suppleness of the skin drop, and skin roughness and fine wrinkles appear.
Hitherto, hyaluronic acid has thus been blended as a moisturizing agent into cosmetics that are applied to the skin, in the expectation that skin moistness will be maintained and skin roughness improved.
However, human skin has inherently a function of protecting the body from external factors, i.e., a biological defense function, and hence it is thought that it is difficult for hyaluronic acid of high molecular weight to pass through the epidermis and reach the corium. Hyaluronic-acid-containing cosmetics thus predominantly utilize the moisturizing effect produced when hyaluronic acid is applied to the skin, and hence the current state of affairs is that an essential effect for improving skin roughness in which the hyaluronic acid acts right inside the skin is not obtained.
It has thus been proposed that hyaluronic acid be put into the body not via the skin but rather by oral ingestion. For example, a foodstuff containing hyaluronic acid and a protein made into peptide form through enzymatic degradation with a protease (Japanese Patent Application Laid-open No. H5-111367 (U.S. Pat. No. 2,787,254)), and a food additive that contains hyaluronic acid of average molecular weight 10,000 to 500,000 and for which the intestinal absorption of the hyaluronic acid is improved (Japanese Patent Application Laid-open No. 2000-102362 etc.), have been proposed.
However, in the case of the hyaluronic acid used in the foodstuff disclosed in Japanese Patent Application Laid-open No. H5-111367, according to the manufacturing method thereof (Examples (paragraphs 0006, 0007)), peptides are intentionally included therein, and hence the degree of refining and the purity of the hyaluronic acid are low. There is thus a problem that, if this foodstuff is used as a food or a food ingredient as is, then discoloration and generation of an unpleasant odor will occur during storage of the food.
Moreover, the hyaluronic acid used in the food additive disclosed in Japanese Patent Application Laid-open No. 2000-102362 is again not high-purity hyaluronic acid as used in cosmetics, but rather cheap unrefined hyaluronic acid intended for use in foods. There is thus a problem that, as above, when this unrefined hyaluronic acid is used, discoloration and generation of an unpleasant odor occur during storage. Moreover, even if refining were carried out, there is still a problem in that skin improving effects as good as those hoped for will not be obtained with hyaluronic acid having an average molecular weight in a range of 10,000 to 500,000.
An object of the present invention is to provide an oral skin improving agent that has hyaluronic acid as a principal component, that exhibits good skin improving effects when orally ingested, and for which the problems of discoloration and generation of an unpleasant odor during storage are suppressed; a food composition for improving skin containing this skin improving agent; and a skin improving method.
The present inventors perfected the present invention after discovering that the above object can be achieved if refined hyaluronic acid having a purity of at least a certain specified value and an average molecular weight within a certain specified range is used as the hyaluronic acid.
Specifically, the present invention provides an oral skin improving agent that comprises hyaluronic acid having a purity of at least 90% and an average molecular weight in a range of 750,000 to 1,200,000.
The present invention also provides a method of improving human skin that comprises the step of having a human ingest the above-mentioned oral skin improving agent, such that the ingestion amount of the hyaluronic acid having a purity of at least 90% and an average molecular weight in a range of 750,000 to 1,200,000 is at least 5 mg per day.
Moreover, the present invention also provides a food composition for improving skin that comprises the above-mentioned oral skin improving agent.